Periodically sell Littler as the crème de la crème (5)
I believe the answer is:
elite
'the creme de la creme' is the definition.
(I've seen this in another clue)
'periodically sell littler' is the wordplay.
'periodically' means one should take alternating letters (letters must be selected 'every so often').
'sell'+'littler'='selllittler'
The alternating letters of 'selllittler' are 'ELITE'.
'as' acts as a link.
(Other definitions for elite that I've seen before include "Superior or favoured group of people" , "12 letters = 1 inch (type)" , "Letter size; superior group" , "Exclusive set" , "Aristocratic" .)